The field of the present invention relates to optical gratings. In particular, highly efficient optical gratings are disclosed herein that include at least one impedance matching layer or are arranged to exhibit reduced polarization dependence.
A wide variety of optical gratings are available for diffracting optical signals, in transmission or in reflection. One particular example is disclosed by Wang et al (“Deep-etched high-density fused-silica transmission gratings with high efficiency at a wavelength of 1550 nm,” Applied Optics, Vol 45 No 12 p 2567 (2006)). The optical grating disclosed therein comprises relatively deep etched grooves in a fused silica substrate (about 2.5 μm deep for maximum diffraction efficiency at 1550 nm). The optical gratings disclosed by Wang et al can be advantageously employed, for example, for dividing or combining optical signals of differing wavelengths in a dense wavelength division multiplexing (DWDM) optical telecommunications system.
It is desirable to provide efficient gratings with reduced thickness (i.e., etch depth) requirements. While the optical gratings disclosed by Wang et al can be highly efficient (calculated>95%, measured>87% for TE polarization), it is nevertheless desirable to provide optical gratings that exhibit increased efficiency, decreased polarization dependence, or decreased wavelength dependence. Such improved optical gratings would find wider applicability in a variety of telecommunications or other optical implementations.